The continuously variable transmission (CVT) has become more widely employed as the technology has developed. The CVT transmission provides for a continuous variation of the transmission ratio between an input shaft and an output shaft, avoiding the necessity of a shifting type transmission, such as a standard shift requiring the engagement and disengagement of sets of gears to provide different gear ratios and an automatic transmission, requiring hydraulic operation of clutches in a planetary gear environment to provide different gear ratios.
A typical CVT transmission will employ an input pulley connected to the input shaft and an output pulley connected to the output shaft, with a continuous endless belt running between the pulleys. The distance between the faces of the pulleys will be varied to change the effective radius of the belt as it travels about the pulleys. The ratio of the effective radius at each pulley determines the transmission ratio of the CVT transmission.
As can be understood, the components of the CVT transmission must be precisely engineered and manufactured for proper operation. A common belt design is of the type having a plurality of trapezoidal shaped transverse elements or load blocks carried on one or more endless flexible carriers formed of nested metal bands. The sides of the transverse elements engage the faces of the pulleys while the carriers provide structure to the belt.
In a common design, the transverse elements have two slots, each slot extending inwardly from one of the pulley engaging faces thereof The transverse elements are mated with a carrier at one of the slots and positioned in a close packed configuration on the carrier side-by-side to fill up the entire length of the carrier. A carrier of equal diameter is then inserted in the slot on the opposite side of the transverse elements. The carriers are confined within the slots through the geometry of the slots and carriers, as well as the faces of the pulleys, to provide structure to the belt. Power is conveyed through the belt with the transverse elements acting against each other, constrained to remain in the belt by the carriers.
Typically, each carrier will be made up of a number of nested bands, for example 8 or 10. Each band in the carrier is of slightly different diameter than the other bands so that they are nested concentrically, typically with a small separation between each band for passage of lubricant.
A typical band utilized in a CVT belt may have a diameter of about eight inches, a width of xe2x85x9c inches and a thickness of about 0.008 inches (8 mils). Such bands are commonly formed from rolling metal sheet material into a tube, laser welding the seam and then cutting individual bands from the tube and roll expanding the bands to the desired final diameter. While this process is effective, a need exists for a more cost effective technique to manufacture high quality bands.
In accordance with one aspect of the present invention, a method is provided for manufacturing bands including the steps of spiral winding thin metal strips into a continuous tube, welding the thin strip along the spiral winding and cutting bands off of the continuous tube.
Further aspects of the present invention include cutting bands off of the continuous tube by laser cutting or by mechanical slitting. The spiral winding can be performed over a mandrel and against feed rollers.
The mechanism for cutting bands off the continuous tube can be moved along the axis of the continuous tube as the tube is manufactured to properly cut the bands. Roll expanding of the bands can occur after they are cut off of the continuous tube or the continuous tube can be roll expanded itself before the bands are cut from the continuous tube.
In another aspect of the present invention, a band is provided which is manufactured by the process set forth above.